1. Field of the Invention
The present invention relates to an image data processing system and method which may be used in an image forming apparatus, using an electrophotographic system processing digital image data, such as an optical printer such as a laser printer, a digital duplicator, a page-printing facsimile device, or an image display device. The present invention in particular relates to image fineness improvement in such apparatus/systems.
2. Related Art
Such image forming device and image display device quantize text image data or picture image data so that the relevant data is expanded into the dot-matrix bit-map format using two-tone data. The text image data is obtained by converting the text code data using font data and the picture image data is obtained by reading in using an image scanner or the like. The bit-map format of the relevant data is formed stored in video memory area in a RAM (random access memory) and is then read out sequentially to be supplied as video data to an image forming unit (engine) or to an image display unit. The image forming unit forms the corresponding image on a recording medium such as a sheet of paper or the like and the image display unit displays the corresponding image on a screen.
An ideal image is an analog image an outline of which may extend in any arbitrary direction continuously. However, such a bit-map image obtained as a result of quantization is a digital image an outline of which may extend in the predetermined two perpendicular dimensions of the dot matrix. If an outline of the digital image extending obliquely or curvedly should be expressed, it is necessary for the outline to extend stepwise along the dot-matrix ruled lines (such phenomenon may be referred to as `jag`) generally obliquely or curvedly. This inevitable property of the digital image may degrade the fineness of the final image, that is, may disable precise representation of an original image or may disable precise representation a desired outline.
Reduction in dot (pixel) size of the dot matrix, that is, increasing the number of dots present in a unit area (increasing the dot-matrix resolution) may reduce such image degradation. However, such resolution increasing raises the cost by a great amount. In one example, obtaining of 600.times.600 dpi two-dimension bit-map as a result of doubling the resolution of the 300.times.300 one requires 4 times increase in the memory capacity and 4 times the processing speed increase of the data processing capability.
Other measures for reducing image degradation include interpolation technology which produces a line connecting between adjacent angular edges present on a stepwise outline so as to form a slope therebetween. Another aspect of the interpolation technology smooths brightness between adjacent outline dots so as to make the edge unclear. However, such measures are effective to smooth jags on an outline but may degrade contrasts and/or resolution since fine shapes are made unclear.
In order to solve such a problem, technology has been developed as disclosed in the U.S. Pat. No. 4,544,922. In this technology, a dot having a size smaller than the ordinary size is added or a partial area having the above smaller dot side is removed from an appropriate part of a dot pattern represented by a bit map so as to correct the relevant part. A pattern recognition technology and/or template comparison technology are used to detect a part to be corrected in the dot pattern. The above disclosed technology performs the pattern recognition process or the template comparison process on all the positions of a bit-map image and performs dot correction such as described above appropriately. As a result, although it is possible to improve image quality (image fineness) by smoothing a line shape without degrading contrasts, the relevant processing system is extremely costly and requires very long time.
In order to solve the problem, Japanese Laid-Open Patent Application No. 2-112966 has proposed a method. In this method, a relevant bit-map image is compared with a previously stored predetermined template for each small fragment of the images. Then, if matching in characteristics is detected between the bit-map image and a template for an image fragment, the fragment of the bit-map image is corrected by correction dots. Thus, the image quality in printed images is improved.
In order to realize the above method, a template matching process described below is performed for example. The data of the bit map is converted into the serial data so as to be input to a FIFO (first in first out) buffer, and a subset of the bit-map image of N.times.M bits is formed. A sample window is used to observe or extract there through data from the subset of bit-map images, which window has a predetermined shape, has a predetermined number of bits and has a central bit corresponding to that of the subset image. Then, the thus observed/extracted data is used to detect matching with templates having various characteristics patterns which patterns are ones of images to be corrected.
If any template matches the observed/extracted data, a certain correction subcell (correction dot) is used to replace the central bit in the relevant subset image. The correction subcell corresponds to the relevant template. If no template matches the observed/extracted data, the relevant central bit is left unchanged.
Such template matching processes are performed by sequentially shifting the subset image to be processed so that all the area of the relevant bit-map image is processed. The processes are performed so that each bit of the bit-map image is assigned to the above central bit sequentially. Thus, in comparison with the above technology disclosed in the United States Patent, a fine final image may be obtained by improving the image quality even with a relatively small memory capacity and with a relatively inferior data processing capability.
However, even in the above method, a great number of templates in the above sample-window formation are necessary corresponding to all the characteristic patterns of images. Matching patterns included in a relevant given bit-map image should be corrected. If such templates should be provided corresponding to all arbitrary shapes of images, the number of templates should be a considerable one. Producing the number of templates requires a considerable manpower and thus requires considerable cost. Further, a considerable capacity of memory is required to store the number of templates. Further, the above described template matching processes require a considerable time.
In order to solve the problems, a person among the inventors of the present invention, together with other persons, has disclosed picture data processing method and its device in Japanese Laid Open Patent No. 5-207282.
The above method can correct jags such as described above so as to improve a resulting image quality using input image data in a bit-map formation. The method can reduce data which should be previously stored in a memory, which data will be used to perform an appropriate correction process on the bit-map image. The method carries out the determination of dots in the input image data to be corrected and the determination of the corresponding correction manners to be applied to the correction-required dots. The method carries out the above determination by means of simple logical operations with an extremely short time period using a microprocessor.
This method will now be briefly described. The method recognizes the characteristics of the line shape of the boundary between a black-dot region and a white-dot region in the bit map of an input image data. As a result, the characteristics are then converted into a multi-bit code for each dot of the input image data. Then, at least a part of the code is used to determine whether or not the relevant dot is one to be corrected. Then, if the dot is determined to be corrected, it is corrected in accordance with manners determined depending on the relevant code. The above determination uses a pattern memory having addresses corresponding to the codes, wherein the appropriate manners to be used for the correction may be determined according to the addresses.
Each of the above code includes a code indicating the slope direction of the line at the position of the relevant dot, a code indicating a manner of the sloping, and a code indicating a position of the relevant dot. The above position is one, the origin of which is the initial dot in the series of dots straightly arranged vertically or horizontally and including the relevant dot.
In the above method, it is not necessary to provide and store as templates all characteristic patterns, corresponding to ones to be corrected. The method can carry out the determination of dots to be corrected and the determination of the manners of correction for the correction-required dots simply and within a short time period using the codes which can be produced easily, described above.
Further, dot data of dots present in an area, the center of which is the relevant dot, is extracted through an appropriate window. The area is separated into a core area located at the center and a plurality of peripheral areas located peripheral of the core area. The above code is produced based on recognition information obtained as a result of recognizing the line shape as mentioned above. The recognition information to be used to produce the code is the combination of core-area recognition information and peripheral-area recognition information. The core-area recognition information is obtained using the core area of the image data and the peripheral-area recognition information is obtained using at least one peripheral area of the image data. At least one peripheral area is determined using the core area of the image data. Thus, it is possible to reduce the amount of information to be used in the production of the above codes so that the code production can be carried out efficiently.